The present invention relates to organic UV absorbers which are soluble in polar media, to lacquer systems prepared therefrom, and to coatings containing such UV absorbers, and to finished parts protected by protective lacquers containing such UV absorbers.
For exterior use, plastics or natural materials (wood) must be protected against photochemical degradation with a suitable coating. To that end, UV-protective agents are added to the plastics themselves, or the materials are provided with covering/protective layers containing UV-protective agents. A very good class of UV absorbers according to the current prior art are biphenyl-substituted triazines (WO 2006/108520 A). This class of substances exhibits an excellent absorbing action at 320-380 nm and at the same time very high intrinsic UV stability (WO 2000/066675 A1, U.S. Pat. No. 6,225,384). Because of their very pronounced aromatic nature, the substances of this class known hitherto are readily soluble only in non-polar and medium-polar media, which is sufficient for most UV-curing protective lacquers based purely on organic substances. It is known that such lacquer layers do not have sufficient scratch resistance. This limits considerably the applications of the systems in the exterior sector, such as, for example, in the architectural sector, and prevents completely some exterior applications, for example as automotive glazing in the driver's field of vision.
If, however, the material is also to be effectively protected against wear and scratches by the protective layer, sol-gel silicate lacquers (see e.g. EP-A 0 339 257, U.S. Pat. No. 5,041,313) and other hybrid lacquers (EP-A 0 570 165) are current prior art. The property profile of the organosilane-based lacquers additionally includes excellent weather and light stability, resistance to heat, alkali, solvents and moisture. However, non-polar additives are not soluble in such lacquer systems; commercially available moderately polar, mostly hydroxy-containing UV absorbers and/or inorganic UV absorbers, such as titanium dioxide, zinc oxide or cerium dioxide, are used as UV absorbers, but these do not have the optimum action (EP-A 0 931 820). UV absorbers modified with an alkoxysilyl(alkyl) group for such resorcinol-based lacquer systems have been disclosed in U.S. Pat. No. 5,391,795 and U.S. Pat. No. 5,679,820. However, the mono-modification described therein cannot be transferred to biphenyl-substituted triazines either in terms of the synthesis route or in terms of effect. U.S. Pat. No. 7,169,949 discloses triazine-based UV absorbers which are modified with a silane group. However, the monoalkoxysilyl-substituted triazines described and shown therein do not carry biphenyl substituents. The use of those triazines in organic coating compositions is described. Organic-inorganic hybrid lacquers, in particular sol-gel coatings, are not mentioned, however. As is shown hereinbelow, these monoalkoxysilyl-substituted triazines are not soluble in such lacquers. Moreover, the polar-modified triazines shown here cannot be prepared by the synthesis route proposed in U.S. Pat. No. 7,169,949. Furthermore, the UV-protective action of the non-biphenyl-substituted triazines described therein is not optimal for polycarbonate in particular.
Suitably polar-modified UV absorbers from the substance class of the triazines and their use in lacquer systems, such as hybrid lacquers, in particular sol-gel silicate lacquers, are accordingly not known hitherto.